1. Field of the Invention
The invention relates to the field of monitoring movement of traffic along predetermined routes, where individual moving elements can move with a high degree of discretion as to speed except when congestion, accident or the like limit speeds. In particular, the invention is applicable to monitoring the flow of motor vehicles along urban or suburban roads and highways which are subject to delays of sufficient frequency and severity that corrective action or dissemination of information announcing a delay are economically desirable.
The principle of the invention is applicable to any situation in which movement is primarily limited to forward progress along a defined path or guideway, or transfer at intersections with other defined paths or guideways, and where there are limitations on the possibility of dodging around slowly moving or stopped elements. Thus, as used in the following description and claims, the term "vehicle" should be broadly interpreted and is not limited to wheeled vehicles or objects moving on land surfaces.
Information about traffic flow, and particularly about unusual deviations from the flow which would be "normal" or expected for that route at that time and the general area weather conditions, allows emergency vehicles to be dispatched to trouble spots before specific reports of accidents or the like are available; allows people or vehicle operators to choose alternate routes to avoid delays; and can be invaluable for improving the accuracy of traffic engineering studies.
2. Description of the Prior Art
Since telephone service has become widely available, volunteer anecdotal reporting of abnormal conditions has been one of the most important sources of information about highway traffic flow. Aerial scanning by reporters in small planes is highly effective for the relatively limited areas which can be viewed in any period of time, but this is quite expensive and becomes inoperative when weather conditions make it most valuable. Surveillance devices such as TV cameras can provide information on all lanes of a multi-lane roadway at one location, but have a high unit cost, and are a target for theft or vandalism. Further, none of the systems described above provide outputs which are readily processed by computers.
Direct speed measuring devices, such as Doppler radar, are quite expensive. While they can readily provide outputs which can be received and processed by computers, they may not provide accurate data for stop-and-go traffic in a traffic jam.
Simple, low cost detectors can be used, but they do not usually provide speed data directly. For example, inductive pick-up loops can be installed in highway surfaces, with connections to a central processor. Such a system is shown summarily in a brochure for "California PATH", University of California, Bldg. 452 Richmond Field Station, 1301 S. 46th Street, Richmond, Calif. 94804. However, not only is it expensive to install a sufficient number of such sensors along any one highway, communication of the sensors with the central processor will require a great amount of cabling, or dedication of a substantial transmission spectrum. Local processing, to provide accurate speed data independent of the size of or space between vehicles, may be required, thereby increasing installation and maintenance cost considerably. Further, the sensor/communication failure rate has been estimated to be about 20% per year. Buried sensors require disturbances in the road surface and underlayment, and thus can be a cause of accelerated roadway deterioration. As a result the relatively high cost of fixed monitoring devices, and the continuing cost of communication with each of them, preclude installing such devices at a sufficient number of locations to provide detailed information for a large area.
Many organizations are now involved in planning, studies and tests of systems for improving the flow or safety of highway travel. Over 40 of these are referred to in Strategic Plan for Intelligent Vehicle-Highway Systems in the United States, Report No. IVHS-AMER-92-3, published by the Intelligent Vehicle-Highway Society of America. Particular projects involving collection of traffic flow information include PATH (referred to above), GUIDESTAR (Minneapolis, Minn.), TRAVTEK (Orlando, Fla.; already completed) and ADVANCE (Chicago, Ill.). However, none of these have proposed a system for accurate deviation-oriented data collection and dissemination which can minimize the required volume of communications on a day-to-day basis.
Partly because of the high installation costs which would accompany the systems proposed to date, the highway traveler today seldom sees any example of high-technology traveler information systems. Recently, major highways in many areas have signs urging motorists to report accidents via cellular telephones; this method of collecting information avoids high costs of installing equipment which will be little utilized, and can provide coverage of almost every significant event. However, it suffers the problem that some problems are reported by too many people, thereby tying up communications channels and the dispatchers who receive the information; some problems are not reported at all; and anecdotal reporting is subject to severe quantitative inaccuracy because of subjective interpretation and the fact that drivers are too involved with driving their vehicles to note average speeds or the location with sufficient accuracy.